This invention relates to a polyol composition containing a particulate filler, more particularly to a stable dispersion of a particulate filler in a polyol, as well as to a polyurethane prepared therefrom.
It is often desirable to "fill" polymeric material with an inert filler. In many instances, the filler provides desirable physical properties or simply reduces the overall cost of the polymeric article. Polyurethanes, like other polymers, are often filled for these and other purposes. In particular, polyurethane coatings and polyurethane carpet backings are often filled.
Typically, the filler is incorporated into a melt of the polymer, and is easily kept homogeneously dispersed therein by solidfying the polymer. The solid state of the polymer keeps the filler from settling out. Unlike most other polymers, however, polyurethane polymers usually are polymerized and shaped or molded at the same time. Accordingly, the filler is typically incorporated in the polyurethane by blending it into one or more of the precursor materials. Most often, the filler is blended with the active hydrogen-containing materials.
Unfortunately, the fillers are often not easily and stably dispersable in the polyether polyols most often used in making polyurethanes. This is particularly true when the polyether polyol contains a significant proportion of repeating oxyethylene units. Commonly used fillers such as alumina trihydrate, barium sulfate and calcium carbonate tend to settle out of these polyether polyols during handling. This causes a myriad of problems, such as clogged lines, precipitate cakes in storage tanks, and inconsistent composition of the polyol mixture. This last problem is particularly bothersome, since the stoichiometry of the reaction between the polyol mixture and the polyisocyanate will change as the composition is consumed. This leads to undercured or overcured products having undesirable properties.
With many polymer dispersions, such as latexes, the filler can be dispersed and stabilized therein with the use of a thickener. However, since the polyol is of substantial viscosity to begin with, the use of these thickeners tends to make the compositions too viscous to handle easily.
The problem of filler suspension instability is of particular concern in making polyurethane-backed carpet, especially unitary carpet backing. The polyurethane used in this application contains a high level of fillers. In addition, due to the exacting performance specifications, the composition of the polyol mixture must be the same, within very low tolerances, during the course of a run. As a result, it has become very important to provide improved stability to polyol mixtures containing particulate fillers.
Titanate compounds and silane coupling agents are known to be useful in stabilizing particulate fillers in organic polymers. However, their use in polyurethanes has at least one substantial disadvantage. In coupling with the filler particles, these agents form a monoalcohol. This alcohol reacts with a polyisocyanate to form an end to the growing polymer chain. Accordingly, it causes the average molecular weight of the polyurethane to be substantially reduced, which in turn causes inferior physical properties.
Fatty acids are also known as dispersing agents for particulate fillers. However, these materials greatly reduce the reactivity of the polyurethane precursor, making them unsuitable for use in polyurethanes.
Accordingly, it would be desirable to provide a dispersion of a particulate filler in a polyether polyol which has improved stability, i.e., in which the filler particles have improved resistance to precipitation.